Method and apparatus for removing hot pixels in a digital camera

ABSTRACT

An apparatus and method of removing fixed pattern noise in a digital camera are provided. The apparatus includes a signal processing unit that calculates location information of the fixed pattern noise from a dark image photographed using an ISO and exposure time that are different from an ISO and exposure time used to photograph a general image, and removes the fixed pattern noise from the general image using the location information. The fixed pattern noise can be effectively removed while reducing the total photographing time in comparison to conventional apparatuses and methods.

BACKGROUND OF THE INVENTION

This application claims the priority of Korean Patent Application No.10-2004-0087799, filed on Nov. 1, 2004 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

1. Field of the Invention

The present invention relates to methods and apparatuses for operating adigital camera, and more particularly, to methods and apparatuses forremoving hot pixels from a photographic image in which a dark frame istaken using an ISO and an exposure time that are different from thatused in the photographic image.

2. Description of the Related Art

Digital imaging devices such as digital cameras and digital camcordersuse charged coupled devices (CCDs) in place of film. A CCD is a sensorthat converts light into electric signals. It has a silicon chip withminute photodiodes disposed on top of it. These photodiodes areorganized into numerous “pixels” on top of the silicon chip in acheckered pattern. Each pixel of the CCD captures light that iseventually converted into one “pixel” of an image.

CCDs are sensitive to heat. As a result, heat noise is frequentlygenerated when a CCD operates, which prevents a cell from accuratelygenerating the color for its pixel. Pixels generated by CCDs as a resultof this heat noise are called hot pixels. Hot pixels usually show up ata fixed location for a short period of time. That is why hot pixels arealso called “fixed pattern noise.” Fixed pattern noise frequently occurswhen the shutter of a digital camera is open for a long period of time,and it hinders the smooth reproduction of an image.

FIG. 1 is a flow chart illustrating a conventional method of removingfixed pattern noise. First, an image frame (Frame 1) is photographedaccording to a set CCD sensitivity (ISO) and exposure time (100). Theimage frame (Frame 1), including the fixed pattern noise, is stored in amemory (not shown) (102). Then, a so-called “dark frame” (Frame 2) isphotographed using the same ISO and exposure time as the photographedimage frame (Frame 1) (104). A dark frame (such as Frame 2) is an imagephotographed with the shutter manually closed to physically block alllight from reaching the CCD. The dark frame (Frame 2) is not affected bylight but does include the fixed pattern noise.

The same exposure time is used when photographing the image frame (Frame1) and the dark frame (Frame 2), so as to accurately reproduce the fixedpattern noise of in the image frame (Frame 1) on the dark frame (Frame2). Ideally, the same number n hot pixels will occur on both the imageframe (Frame 1) and the dark frame (Frame 2).

The photographed dark frame (Frame 2) is then stored in the memory(106). Frame subtraction is then performed to remove the fixed patternnoise. That is, the dark frame (Frame 2) is subtracted from the imageframe (Frame 1) (108). Through such frame subtraction, a new image frame(Frame 3) with the fixed pattern noise removed is generated. The newimage frame (Frame 3) is then corrected by image processing, and animage file (e.g., JPEG) is generated (110).

The method illustrated in FIG. 1 the total photographing time is morethan twice the set exposure time of the digital image processingapparatus. For example, referring to FIG. 6A (which illustrates thetotal photographing time of a conventional digital image processingapparatus) if the exposure time is 10 seconds, {circle around (1)} theimage frame (Frame 1) is photographed for 10 seconds, {circle around(2)} the dark frame (Frame 2) is photographed for 10 seconds, {circlearound (3)} the noise removal after frame subtraction takes s1 seconds,and {circle around (4)} the post-processing of the frame subtractiontakes s2 seconds. Consequently, the total photographing time ({circlearound (1)}+{circle around (2)}+{circle around (3)}+{circle around (4)})is more than twice the exposure time, that is, more than 20 seconds.Thus, it can be seen that there is a need for a new method and apparatusfor removing noise from a digital image that avoids the foregoingproblems.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for removing fixedpattern noise in a digital camera that removes fixed pattern noise whilereducing the total photographing time by photographing a dark image withgreater sensitivity and shorter exposure time than an original image andremoving the fixed pattern noise from the original image by calculatinglocation information of the fixed pattern noise from the dark image.

According to an embodiment of the invention, an apparatus comprises asignal processing unit that receives signals representing a firstphotograph, in which the first photograph was taken at first ISO and ata first exposure time. The apparatus also receives signals representinga second photograph, in which the second photograph is a dark imagephotographed at a second ISO and at a second exposure time, the secondISO being different from the first ISO, and the second exposure timebeing different from the first exposure time. The signal processing unitanalyzes the dark image, calculates the location of the fixed patternnoise based on the analysis, and removes the fixed pattern noise fromthe photograph using the calculated location.

In various embodiments of the invention, the second photograph isphotographed using an ISO that is N times the ISO used to photograph thefirst photograph, and using an exposure time that is 1/N the exposuretime used to photograph the general image.

In another embodiment of the invention, a method of removing fixedpattern noise in a digital camera, comprises photographing a main imageusing a first ISO and a first exposure time; photographing a dark imageusing a second ISO and a second exposure time, wherein the second ISO isdifferent from the first ISO, and the second exposure time is differentfrom the first exposure time; determining the location of the fixedpattern noise in the dark image; using the determined location to removethe fixed pattern noise from the general image.

In yet another embodiment of the invention, a method for removing fixedpattern noise comprises setting the digital camera to a first ISO and afirst exposure time; opening a shutter of a digital camera to permitlight to enter the digital camera; receiving the light with acharge-coupled device; capturing a first image with the charge-coupleddevice; setting the digital camera to a second ISO and a second exposuretime; closing the shutter to prevent light from entering the digitalcamera; capturing a second image with the charge-coupled device whilethe shutter is closed; determining, using a digital signal processor,the location of the fixed pattern noise on the second image; alteringthe content of the first image at a location on the first image thatmatches the determined location on the second image, thereby removingthe fixed pattern noise from the first image; and displaying the firstimage on a display panel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a flow chart illustrating a conventional method of removinghot pixels;

FIG. 2 is a front perspective view of a digital camera according to anembodiment of the present invention;

FIG. 3 is a rear view of the digital camera of FIG. 2;

FIG. 4 is a block diagram of the digital camera of FIGS. 2 and 3;

FIG. 5 is a block diagram of an apparatus for removing fixed patternnoise in the digital camera according to an embodiment of the presentinvention;

FIGS. 6A and 6B illustrates total photographing times of a conventionaldigital camera and a digital camera according an embodiment of thepresent invention; and

FIG. 7 is a flow chart illustrating a method of removing fixed patternnoise in a digital camera according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which embodiments of the invention areshown.

Referring to FIG. 2, a digital image processing apparatus 1 includes amicrophone MIC, a self-timer lamp 11, a flash 12, a view finder 17 a, aflash light amount sensor (FS) 19, and a lens unit 20 on its front; ashutter 13, a mode dial 14, a function-select button 15, aphotograph-information displaying unit 16, and a function-block button18 on its top; and an external interface 21 on its side.

The self-timer lamp 11 operates from a time when the shutter 13 ispressed until the shutter 13 starts operating in a self-timer mode. Themode dial 14 is used by a user to select various operating modes, suchas a still image photographing mode, a night scene photographing mode, amoving picture photographing mode, a play mode, a computer connectingmode, and a system setting mode. The function-select button 15 is usedby the user to select one of, for example, a still image photographingmode, a night scene photographing mode, a moving picture photographingmode, and a play mode of the digital image processing apparatus 1.

The photograph-information displaying unit 16 displays information oneach photographing function. The function-block button 18 is used by theuser to select one of the functions displayed on thephotograph-information displaying unit 16.

Referring to FIG. 3, the back of the digital image processing apparatus1 a includes a speaker SP, a power button 31, a monitor button 32, anautomatic focus lamp 33, a view finger 17 b, a flash standby lamp 34, adisplay panel 35 (e.g., a liquid crystal display (LCD)), an exposurecompensation/delete button 36, an enter/play button 37, a menu/OK button38, a wide-angle zoom button 39 w, a telephoto zoom button 39 t, anup-movement button 40 up, a right-movement button 40 ri, a down-movementbutton 40 lo, a left-movement button 40 le, and a playback button 42.

The monitor button 32 is used by the user to control the operation ofthe display panel 35. For example, if the user presses the monitorbutton 32 a first time, an image of a subject (i.e. the physical scenebeing viewed and photographed by the user) and photographing informationfor the image are displayed on the display panel 35, if the monitorbutton 32 is pressed a second time, only the image of the subject isdisplayed on the display panel 35, and if the monitor button 32 ispressed a third time, power supplied to the display panel 35 is cut off.

The automatic focus lamp 33 operates when an automatic focusingoperation is completed. The flash standby lamp 34 operates when theflash 12 (see FIG. 2) is on standby. The exposure compensation/deletebutton 36 controls the amount of light when the digital image processingapparatus 1 is manually operated, or is used as a delete button when theuser is setting the operating mode.

The enter/play button 37 is used by the user to input data or performvarious functions, such as stop or play in the play mode. The menu/OKbutton 38 is used to display and select a menu of a mode selected by themode dial 14. The up-movement button 40 up, the right-movement button 40ri, the down-movement button 40 lo, and the left-movement button 40 leare used by a user to select the modes and to change displayed region ofthe image displayed on the display panel 35. The playback button 42 isused to check and reproduce the last photographed image, moving picture,or audio information.

Referring to FIG. 4 the digital image processing apparatus 1 (from FIGS.2 and 3) includes an optical system OPS. The optical system OPS includesthe lens unit 20 from FIG. 2, and optically processes light reflectedfrom a subject. The lens unit 20 of the optical system OPS includes azoom lens, a focus lens, and a compensation lens (not shown).

If a user presses the wide-angle zoom button 39 w (see FIG. 3) or thetelephoto zoom button 39 t (see FIG. 3), a signal corresponding to thewide-angle zoom button 39 w or the telephoto zoom button 39 t is inputto a micro-controller 512. Accordingly, the micro-controller 512controls a lens driving unit 510, which drives a zoom motor M_(Z),which, in turn, moves the zoom lens. That is, if the wide-angle zoombutton 39 w is pressed, the focal length of the zoom lens is shortened,thus increasing the viewing angle. Conversely, if the telephoto zoombutton 39 t is pressed, the focal length of the zoom lens is lengthened,thus decreasing the viewing angle. Referential character M_(A) denotes amotor to drive an aperture (not shown).

Referring still to FIG. 4, the digital image processing apparatusfurther includes a photoelectric converter (OEC) 500 of a charge coupleddevice (CCD) or a complementary metal oxide semiconductor (CMOS) (notshown) that converts light from the optical system OPS into electricalanalog signals. In the present embodiment, the OEC 500 will often bereferred to as CCD 500 as an example. It is to be understood, however,that the OEC 500 may also be implemented using CMOS.

The digital image processing apparatus further includes a digital signalprocessor (DSP) 507. Algorithms needed for the operation of the DSP 507and for setting data are stored in an electrically erasable andprogrammable read-only memory (EEPROM) 505. The DSP 507 controls atiming circuit 502 to control the operation of the OEC 500 and ananalog-to-digital converter (ADC) 501. The timing circuit 502 iscontrolled by the micro-controller 512. The ADC 501 converts the analogsignals output from the OEC 500 into digital signals. The DSP 507processes the digital signal from the ADC 501 and generates a digitalimage signal, which is divided into a chrominance signal and a luminancesignal. The digital processing apparatus further includes a removablememory card coupled to a memory card interface (MCI) 506.

Referring still to FIG. 4, the digital image processing apparatus alsohas a light emitting unit LAMP, and a flash controller 511. The lightemitting unit LAMP is operated by the micro controller 512 and includesthe operate/self-timer lamp 11 (see FIG. 3), the automatic focus lamp 33(see FIG. 3), and the flash standby lamp 34 (see FIG. 3). The flash 12is operated via a flash controller 511 and the micro-controller 512according to a signal from the FS 19.

The digital image processing apparatus further includes a user inputunit INP. The user input INP includes the shutter 13 (see FIG. 2), themode dial 14 (see FIG. 2), the function-select button 15 (see FIG. 2),the function-block button 18 (see FIG. 2), the monitor button 32 (seeFIG. 3), the exposure compensation/delete button 36 (see FIG. 3), theenter/play button 37 (see FIG. 3), the menu/OK button 38 (see FIG. 3),the wide-angle zoom button 39 w (see FIG. 3), the telephoto zoom button39 t (see FIG. 3), the up-movement button 40 up (see FIG. 3), theright-movement button 40 ri (see FIG. 3), the down-movement button 40 lo(see FIG. 3), and the left-movement button 40 le (see FIG. 3).

The digital image signal output from the DSP 507 is temporarily storedin a dynamic random access memory (DRAM) 504. In an embodiment of theinvention, during the noise removal procedure, a preset number of imageframes of a same image are photographed by the OEC 500 and are stored inthe DRAM 504. The digital image signal output from the DSP 507 is alsoinput to an LCD driving unit 514. As a result, an image is displayed onthe display panel 35, that is, a displaying unit. The digital imagesignal output from the DSP 507 can also be transmitted serially via auniversal serial bus (USB) connector 21 a or an RS232C interface 508 andits connector 21 b, or can be transmitted as video signals via a videofilter 509 and a video outputting unit 21 c.

Referring still to FIG. 4, the digital image processing apparatusfurther includes an audio processor 513, which outputs an audio signalfrom the microphone MIC to the DSP 507 or the speaker SP, and outputs anaudio signal from the DSP 507 to the speaker SP.

Referring to FIG. 5, a block diagram of an apparatus for removing fixedpattern noise in the digital camera according to an embodiment of thepresent invention is shown. Compared to a conventional apparatus forremoving fixed pattern noise, the apparatus illustrated in FIG. 5requires less time to photograph and image, and efficiently removes thefixed pattern noise. The apparatus includes the OEC 500, the ADC 501,the DRAM 504, the DSP 507, the micro-controller 512, the user input unitINP, and the display panel 35 (from FIG. 4). The DSP 507 includes alocation information extractor 507-1, a noise remover 507-2, and asignal processor 507-3.

For example, the user user sets the sensitivity (ISO) and exposure timeof the digital camera 1 via a menu provided by the micro-controller 512and displayed on the display panel 35. In particular, themicro-controller 512 provides a menu for selecting a night scenephotographing mode to set the exposure time. Thus, the user canarbitrarily set the exposure time by selecting the menu for the nightscene photographing mode. In response to the user pressing the shutterbutting, the digital camera 1 takes a photograph, which will be referredto as image frame Frame 1.

When the digital camera 1 takes the photograph, the OEC 500 convertsincident light into electrical signals, and the ADC 501 converts theelectrical signals into digital signals and stores the digital signalsin the first region of the DRAM 504. In this example, it is assumed thatimage frame Frame 1 includes fixed pattern noise.

When the image frame Frame 1 is stored in the DRAM 504, themicro-controller 512 changes a setting of the digital camera 1 inpreparation for taking a second photograph, which will be referred to asdark frame Frame 2. Specifically, the micro-controller 512 changes theISO and the exposure time to photograph the dark frame Frame 2 andphysically blocks all light from entering the OEC 500.

At this time, the micro-controller 512 sets the ISO of the digitalcamera 1 to be N times the ISO used to photograph the image frame Frame1, and sets the exposure time of the digital camera 1 to be 1/N theexposure time used to photograph the image frame Frame 1. Here, N is anatural number.

For example, if the ISO used to photograph an image frame Frame 1 is100, the ISO used to photograph a dark frame Frame 2 is set to 200,which is double the ISO used to photograph the image frame Frame 1. Ifthe exposure time used to photograph the image frame Frame 1 is 16seconds, the exposure time used to photograph the dark frame Frame 2 isset to 8 seconds, which is ½ the exposure time used to photograph theimage frame Frame 1. The dark frame Frame 2 is then photographed andstored in the second region of the DRAM 504.

In the conventional method described above in conjunction with FIG. 1,the same exposure time used to photograph an image frame Frame 1 is alsoused to photograph a dark frame Frame 2, thereby producing the exactsame fixed pattern noise created on both the image frame Frame 1 and thedark frame Frame 2. However, in the present embodiment, image frameFrame 2 is photographing using a different ISO and exposure time thanthat used to photograph image frame Frame 1.

Table 1 illustrates how, as the ISO of the digital camera 1 increases,the exposure time of the shutter 13 is proportionally decreased, theamount of fixed pattern noise created on the dark frame Frame 2increases. The values in Table 1 were obtained experimentally. TABLE 1Digital Shutter Exposure No. of Pixels of camera ISO Time (sec.) FixedPattern Noise 100 16 5990 200 8 7323 400 4 11094

The number of pixels of fixed pattern noise in Table 1 denotes thenumber of pixels having a value greater than a critical value (e.g.,10000) which indicates that the charges in a given pixel are a result offixed pattern noise in the dark frame Frame 2 having a resolution of,for example, 2456×1760.

The dark frame Frame 2 is photographed with N times the ISO used tophotograph the image frame Frame 1 and 1/N the exposure time used tophotograph the image frame Frame 2. Therefore, the dark frame Frame 2includes the fixed pattern noise included in the image frame Frame 1.

The location information extractor 507-1 of the DSP 507 extractslocation information of the fixed pattern noise from the dark frameFrame 2 stored in the second region of the DRAM 504 and stores theextracted location information in the third region of the DRAM 504.

The noise remover 507-2 filters and removes the fixed pattern noise fromthe image frame Frame 1 stored in the first region using the locationinformation of the fixed pattern noise stored in the third region of theDRAM 504.

The noise remover 507-2 uses, for example, a low frequency spatialfilter to remove the fixed pattern noise. For example, the noise remover507-2 can use a median filter which outputs a median value aftercomparing fixed pattern noise with adjacent pixel values.

The signal processor 507-3 performs image processing on a new imageframe Frame 3 with the fixed pattern noise removed to improve thequality of the image. Then, the new image frame Frame 3 is stored inanother region of the DRAM 504 or is displayed on the display panel 35.

Referring to FIGS. 6A and 6B, a comparison of the total photographingtime of a conventional digital camera and the total photographing timeof digital camera 1 is shown. In a conventional method of removing fixedpattern noise using frame subtraction, the total photographing time ismore than double the set exposure time of a digital camera. Thus, thephotographing time increases. For example, referring to FIG. 6A, if anexposure time of 16 seconds is applied to a conventional digital camera,{circle around (1)} image frame (Frame 1) is photographed for 16seconds, {circle around (2)} dark frame (Frame 2) is photographed for 16seconds, {circle around (3)} noise is removed for s1 seconds, and{circle around (4)} post-processing is performed for s2 seconds.Consequently, the total photographing time ({circle around (1)}+{circlearound (2)}+{circle around (3)}+{circle around (4)}) is more than doublethe exposure time, that is, 32+s1+s2 seconds.

However, in the present embodiment of the present invention, the time tophotograph the dark frame Frame 2 is shorter than the time to photographthe image frame Frame 1 (e.g., when quadrupling the ISO, ¼ the exposuretime is used), thereby reducing the total photographing time. Forexample, referring to FIG. 6B, if an exposure time of 16 seconds used,{circle around (1)} the image frame Frame 1 is photographed for 16seconds, {circle around (2)} the dark frame Frame 2 is photographed for4 seconds, {circle around (3)} noise is removed for s'1 seconds, and{circle around (4)} post-processing is performed for s'2 seconds.Consequently, the total photographing time ({circle around (1)}+{circlearound (2)}+{circle around (3)}+{circle around (4)}) takes 20+s'1+s'2seconds, which is less than the total photographing time of theconventional method.

Referring now to FIG. 7, a method of removing the fixed pattern noise inthe digital camera 1 according to an embodiment of the invention willnow be described. First, an image frame Frame 1 is photographed using aset ISO and exposure time (700). For example, the ISO is set to 100 andthe exposure time is set to 16 seconds and the image frame Frame 1 isphotographed. The OEC 500 converts incident light into electricalsignals, and the ADC 501 converts the electrical signals into digitalsignals.

The image frame Frame 1, which is digitalized and includes fixed patternnoise, is stored in the first region of the DRAM 504 (702). Then, themicro-controller 512 changes the ISO and the exposure time set in thedigital camera 1 and photographs a dark frame Frame 2 while physicallyblocking all incident light (704). The micro-controller 512 sets the ISOto be N times the ISO used to photograph the image frame Frame 1 andsets the exposure time to be 1/N the exposure time used to photographthe image frame Frame 1. Here, N is an arbitrary natural number. Forexample, if the ISO is 100 when photographing the image frame Frame 1,the ISO use to photograph the dark frame Frame 2 can be quadrupled to400, and if the exposure time is 16 seconds when photographing the imageframe Frame 1, the exposure time used to photograph the dark frame Frame2 is set to ¼ the exposure time used to photograph the image frame Frame1, that is, 4 seconds. The photographed dark frame Frame 2 is stored inthe second region of the DRAM 504 (706).

As illustrated in Table 1, the number of hot pixels producing the fixedpattern noise in the dark frame Frame 2 increases as the ISO of thedigital camera 1 increases and the exposure time of the digital camera 1decreases. Since the dark frame Frame 2 is photographed with N times theISO used to photograph the image frame Frame 1 and 1/N the exposure timeused to photograph the image frame Frame 1, the dark frame Frame 2includes the fixed pattern noise included in the image frame Frame 1.

The location information extractor 507-1 extracts location informationof the fixed pattern noise from the dark frame Frame 2 stored in thesecond region of the DRAM 504 and stores the location information in thethird region of the DRAM 504. (708).

The noise remover 507-2 filters and removes the fixed pattern noise ofthe image frame Frame 1 stored in the first region of the DRAM 504 usingthe location information of the fixed pattern noise stored in the thirdregion of the DRAM 504 (710).

A low frequency spatial filter such as a median filter is used to removethe fixed pattern noise of the image frame Frame 1 to define a new imageFrame 3, from which the fixed pattern noise is absent. In doing so, themedian filter outputs a median value by comparing the fixed patternnoise and adjacent pixel values.

The signal processor 507-3 performs image processing on the new imageframe Frame 3 to improve the quality of an image. Then, the signalprocessor 507-3 stores the new image frame Frame 3 in another region ofthe DRAM 504 or displays it on the display panel 35 (712).

As illustrated in FIG. 6, the total photographing time is shortenedremarkably in the present embodiment compared to the conventional methodsince the exposure time used to photograph the dark frame Frame 2 is 1/Nthe exposure time used to photograph the image frame Frame 1.

As described above, an embodiment of the present invention photographs adark image by increasing ISO and reducing exposure time of a digitalcamera compared to those used when photographing an original image.Location information of fixed pattern noise is extracted from thephotographed dark image to remove the fixed pattern noise from theoriginal image. Thus, the fixed pattern noise can be effectively removedwhile reducing the total photographing time.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims. The exemplaryembodiments should be considered in descriptive sense only and not forpurposes of limitation. Therefore, the scope of the invention is definednot by the detailed description of the invention but by the appendedclaims, and all differences within the scope will be construed as beingincluded in the present invention.

1. An apparatus for removing fixed pattern noise in a digital camera,the apparatus comprising: a signal processing unit that performs stepscomprising: receiving signals representing a first photograph, whereinthe first photograph was taken at first ISO and at a first exposuretime, and wherein the first photograph includes fixed pattern noise;receiving signals representing a second photograph, wherein the secondphotograph was taken in the absence of light at a second ISO and at asecond exposure time, the second ISO being different from the first ISO,the second exposure time being different from the first exposure time;analyzing the second photograph; calculating the location of the fixedpattern noise based on the analyzing step; and removing the fixedpattern noise from the first photograph using the calculated location.2. The apparatus of claim 1, wherein the second ISO is N times the firstISO, and the second exposure time is 1/N times the first exposure time.3. The apparatus of claim 2, wherein the signal processing unitcomprises: a location information extractor that extracts the locationinformation of the fixed pattern noise from the second photograph; anoise remover that filters the fixed pattern noise from the firstphotograph using the location information; and a signal processor thatprocesses the first photograph to remove the fixed pattern noise therebyresulting in an image that is displayable.
 4. The apparatus of claim 1,further comprising a storage unit, wherein the storage unit includes: afirst region to store the first photograph; a second region to store thesecond photograph; and a third region to store the calculated locationinformation.
 5. The apparatus of claim 1, further comprising: a lens;and a photoelectric converter, wherein the photoelectric converterperforms steps comprising: receives light through the lens to capture animage for the first photograph; receives no light through the lens tocapture an image for the second photograph; converts the captured imagefor the first photograph and the captured image for the secondphotograph into the signals; and transmits the signals to the signalprocessing unit.
 6. The apparatus of claim 5, wherein the photoelectricconverter is a charge-coupled device.
 7. The apparatus of claim 5,wherein the photoelectric converter is a complimentary metal oxidesemiconductor device.
 8. The apparatus of claim 5, further comprising: ashutter that performs steps comprising: opening to permit the light toreach the photoelectric converter to enable the photoelectric converterto capture the image for the first photograph; closing to prevent thelight from reaching the photoelectric converter to enable thephotoelectric converter to capture the image for the second photograph,wherein the first image and the second image each have the fixed patternnoise in the same respective locations.
 9. The apparatus of claim 1,further comprising: a user input unit that receives a user input of thefirst ISO and the first exposure time, wherein the signal processingunit sets the second ISO and the second exposure time based on afunction of the first ISO and first exposure time.
 10. The apparatus ofclaim 1, further comprising: a display that displays the firstphotograph after the fixed noise has been removed by the signalprocessing unit.
 11. A method of removing fixed pattern noise in adigital camera, the method comprising: photographing a main image usinga first ISO and a first exposure time; photographing a dark image usinga second ISO and a second exposure time, wherein the second ISO isdifferent from the first ISO, and the second exposure time is differentfrom the first exposure time; determining the location of the fixedpattern noise in the dark image; and using the determined location toremove the fixed pattern noise from the general image.
 12. The method ofclaim 11, wherein the second ISO is equal to a value that is about Ntimes the first ISO, and wherein the second exposure time is equal to avalue that is about the first exposure time divided by N.
 13. The methodof claim 12, wherein N is a number that is greater than
 1. 14. Themethod of claim 11, further comprising: opening a shutter of the digitalcamera to permit a photosensitive device of the digital camera toreceive light; photographing the main image with the received light,wherein the main image contains the fixed pattern noise; closing theshutter to prevent the photosensitive device from receiving the light;and photographing the dark image while the shutter is closed, whereinthe dark image contains fixed pattern noise at the same location on thedark image as the location at which the fixed pattern noise appeared inthe main image.
 15. The method of claim 14, wherein the second ISO isequal to a value that is about N times the first ISO, and wherein thesecond exposure time is equal to a value that is about the firstexposure time divided by N.
 16. The method of claim 11, furthercomprising: displaying the main image on a display panel of the digitalcamera after the using step.
 17. The method of claim 11, furthercomprising: after the using step, storing, in a memory of the digitalcamera, the main image; and in response to a user input to the digitalcamera, retrieving the main image from the memory and displaying it tothe user on a display panel of the digital camera.
 18. The method ofclaim 17, wherein the display panel is integrated into a housing of thedigital camera, and wherein the memory is located within the housing.19. The method of claim 11, further comprising: receiving, from a uservia a user input unit of the digital camera, a value for the first ISOand a value for the first exposure time; and calculating the second ISOand the second exposure time without any further input from the user.20. A method for removing fixed pattern noise, the method comprising:setting the digital camera to a first ISO and a first exposure time;opening a shutter of a digital camera to permit light to enter thedigital camera; receiving the light with a charge-coupled device;capturing a first image with the charge-coupled device; setting thedigital camera to a second ISO and a second exposure time; closing theshutter to prevent light from entering the digital camera; capturing asecond image with the charge-coupled device while the shutter is closed;determining, using a digital signal processor, the location of the fixedpattern noise on the second image; altering the content of the firstimage at a location on the first image that matches the determinedlocation on the second image, thereby removing the fixed pattern noisefrom the first image; and displaying the altered content of the firstimage on a display panel.